The objectives of this research will be (1) to determine the incidence of renal vein thrombosis (RVT) in infants whose births are complicated by maternal diabetes and/or the development of shock, polycythemia or asphyxia; (2) to determine the natural history of neonatal RVT; and (3) to assess outcome of asymptomatic RVT following supportive care alone versus therapy with heparin anticoagulation.